Project Summary This project will use the multiphase optimization strategy (MOST) approach to test the efficacy of an autonomy supportive behavioral intervention to improve metabolic control among older adolescents and emerging adults (16-25) with T1D. Youth this age demonstrate chronic poor metabolic control that persists into adulthood leading to the premature emergence of short- and long-term diabetes complications. Developmentally, adolescence and emerging adulthood is a time when the need for independence and autonomy are particularly salient. This new intervention will leverage youths? desire for autonomy by designing an intervention to support diabetes self-management autonomy. This intervention is guided by self-determination theory (SDT) which suggests that autonomous (i.e., self-initiated, driven by intrinsic versus extrinsic motivation) diabetes management depends upon three conditions: 1) the perception that one?s behavior is self-directed, 2) feelings of competence, or self-efficacy, and 3) the existence of caring relationships supportive of the behavior. We have identified three intervention components that target the SDT constructs. A question prompt list (QPL) is a simple, inexpensive tool comprised of a list of questions that patients might consider asking their health care provider during a clinic visit. QPLs empower patients to assume a more active role (asking questions and stating concerns) during clinic visits. The Motivation Enhancing System (MES) is an eHealth intervention to increase intrinsic motivation for health behavior change. MES content is based on the Motivational Interviewing (MI) framework and the Information-Motivation-Behavioral Skills (IMB) model of health behavior change which posits that behavior change results from the joint function of three critical components: accurate information about risk behaviors or their replacement health behaviors, motivation to change behavior, and behavioral skills necessary to perform the behavior (self-efficacy). Text message reminders (TXT) are a strategy to encourage youth to complete their diabetes self-care that also lead to gains in self- efficacy and a stronger relationship with diabetes care providers through greater communication and satisfaction. We will test the efficacy of these intervention components toward improving metabolic control in a component selection experiment (N=320). The experiment will use a factorial research design with random assignment to determine which intervention components contribute to a clinically significant improvement (?0.5%) in HbA1c. The result of this research will be an optimized, multi-component intervention with effect size estimates that will be used to inform a large scale, fully powered effectiveness trial. This theory-driven intervention will be scalable to a variety of chronic illness contexts and the knowledge gained from this research will inform self-determination theory and behavioral interventions targeting this population (for which there currently are none).